1. Field of the Invention
The present invention relates to an apparatus for sputtering coatings onto substrate deposition surfaces, particularly to sputtering multi-component metal alloy films onto the substrate, such as a copper-magnesium alloy film having high magnesium content. The invention relates specifically to a magnetron sputter target for use in physical vapor deposition of thin films on semiconductor substrates, and a method for making the same.
2. Description of Related Art
Thickness uniformity and structural integrity are increasingly important for sputtered coatings in physical vapor deposition processes. Modern sputtering is typically done with magnetron cathodes. In a magnetron cathode, the target erosion rate is highest where the magnetic field is parallel to the target surface. A disadvantage of planar magnetrons in which the target is essentially a flat surface is that the magnetic field lines must pass uniformly through the entire target. However, typically there remains a central portion that receives little or no sputtering. This makes uniform sputtering of the planar target extremely difficult. Different magnetron sputtering cathode shapes have been employed to eliminate the deficiencies in planar magnetrons. Conical, cylindrical and other sputtering target geometries have been introduced to mitigate many of the detrimental effects of planar target sputtering. In U.S. Pat. No. 6,093,293 issued on Jul. 25, 2000 to Haag, et al., entitled xe2x80x9cMAGNETRON SPUTTERING SOURCE,xe2x80x9d a sputter source having at least two electrically mutually isolated stationary bar-shaped target arrangements mounted one along side the other and separated by respective slits, was introduced as a means for depositing a homogeneous film on a substrate. The electrically mutually isolated stationary targets were designed to eliminate the effects of erosion furrows created by the tunnel-shaped magnet fields applied to the target along specific courses.
Problems arise when different combinations of metal alloys are required for deposition. For example, thin films of copper-magnesium (CuMg) alloys for integrated circuit applications may require magnesium concentrations in excess of approximately 2 atomic percent. Advanced devices calling for ultra-thin liners on the order of less than 200 Angstroms, deposited on dielectric material such as silicon dioxide and the like, will require a higher magnesium content to permit a reliable magnesium oxide (MgO) based diffusion barrier approximately 20 angstroms thick to form at the copper-magnesium/silicon dioxide (CuMg/SiO2) interface. Fabrication of a CuMg alloy target is problematic since the hardness of a CuMg alloy increases greatly when the magnesium concentration exceeds approximately 4 atomic percent. This makes it impractical to fabricate a high magnesium concentration copper-magnesium target, in either a planar or three-dimensional configuration, e.g., a hollow cathode magnetron (HCM) target. Although CuMg alloy targets with magnesium concentrations as high as 4 atomic percent have been developed, the resulting CuMg films deposited on the semiconductor substrates typically contain much less magnesium, on the order of five to ten times less magnesium, than in the targets primarily due to two factors. The first factor concerns the inefficient transport of the sputtered magnesium to the wafer. The sputtered magnesium is predominantly scattered when combined with argon gas during transport. The second factor concerns a low effective sticking coefficient at the growing CuMg film. Thus, in order to obtain bulk magnesium concentrations in the deposited film in excess of two atomic percent under the conditions generally present in prior art techniques, a metal alloy target with a much greater magnesium concentration is required in order to obtain a CuMg film with a high percentage magnesium content.
Another problem with physical vapor deposition (PVD) is the deposition of a conformal film onto high aspect-ratio features that requires a directional, ionized PVD approach. Unfortunately, the ionization probability and transport of copper and magnesium are different so that a uniform alloy target may not be able to provide acceptable global uniformity for both component alloys over the wafer surface. Similar problems exist for other Cu alloy combinations other than CuMg, such as CuAl, CuCo, CuSn, as well as other (non Cu-based) metal alloy systems. Similarly, preparation of ternary alloys such as COWB is equally affected by the aforementioned problems.
In U.S. Pat. No. 6,312,574 issued on Nov. 6, 2001 to Quaderer et al., entitled xe2x80x9cTARGET, MAGNETRON SOURCE WITH SAID TARGET AND PROCESS FOR PRODUCING SAID TARGET,xe2x80x9d a ferromagnetic magnetron target was introduced containing a pattern of blind holes with a circular cross-section distributed along the sputtered surface. The holes were worked into the target plate by drilling. The distribution of the provided blind holes in the target sputtering surface influences the tunnel field in the targeted manner in order to provide a useful sputtering off-rate distribution and a desired erosion profile. Although the shape of the sputtering target is significantly altered by the blind holes for the deposition of ferromagnetic material, there is no compensation through target geometry for distributing a higher content of one metal alloy over another from a target composed of different metals.
In U.S. Pat. No. 6,309,516 issued on Oct. 30, 2001 to McLeod, entitled xe2x80x9cMETHOD AND APPARATUS FOR METAL ALLOT SPUTTERING,xe2x80x9d a target comprised of two parallel, elongated segments was positioned immediately adjacent the entrance/exit aperture of the process chamber. Although two separate metals were used as this target, neither metal was inlaid within the other in a geometrical pattern in such a manner as to provide uniform film deposition.
In U.S. Pat. No. 6,206,985 issued on Mar. 27, 2001 to Onishi et al., entitled xe2x80x9cAl ALLOY FILMS AND MELTING Al ALLOY SPUTTERING TARGETS FOR DEPOSITING Al ALLOY FILMS,xe2x80x9d the melting aluminum alloy sputtering target was manufactured through the processes of melting and casting, so that part of the other combined metal, e.g., titanium, Zr, Hf, V, and Nb, is dissolved in a solid solution in the Al matrix, creating a homogeneous metal composition. Neither metal is inlaid within the other in a geometrical pattern designed to provide for or enhance uniform film deposition.
In securing sputter targets to backing plates, bonding materials such as Indium (In) are routinely used. In the construction of metal alloy composite targets, e.g., CuMg alloys, the consideration of eliminating unwanted wicking becomes important since the inlaid metals have more adjoining sections than typically found in homogeneous targets, and thus, more opportunities for the bonding material to wick and eventually become part of the deposited film. For a composite target, it is necessary to avoid wicking of the bonding material between the composite plates since this leads to surface contamination of the target, leading to eventual incorporation onto the chamber and the film. Any implementation of a composite metal alloy target structure must consider and reduce the potential for unwanted wicking.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a planar target or a hollow cathode magnetron target that allows for a high concentration of alloying elements, thereby providing for high concentration of the alloying elements in the deposited alloy films.
Another object of the present invention is to provide a composite target that can produce an acceptable global uniformity for all the component elements of the target over the wafer surface.
A further object of the invention is to provide a sputter apparatus for producing multi-component metal alloy films with a high concentration of one of the metals from the target metal alloy structure.
It is another object of the present invention to provide a planar target or a hollow cathode magnetron target that allows for a very high magnesium content to produce high-magnesium CuMg films, typically having a magnesium atomic percentage greater than about four.
It is yet another object of the present invention to provide a sputter apparatus in which the areal percent of the target metal alloy can be kept constant or varied from center to edge in a predetermined way to allow ionized physical vapor deposition to produce a film of uniform thickness and stoichiometry on a semiconductor wafer.
A further object of the invention is to provide target fabrication techniques that permit the PVD films to be deposited with high-purity and with repeatable film uniformity and composition during target life.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The above and other advantages, which will be apparent to those skilled in art, are achieved in the present invention, which is directed to a sputter target apparatus for a magnetron cathode adapted to allow for a controlled sputtering process and produce a uniform metal alloy film on a semiconductor substrate having a target comprising a top surface, an outer edge, and a plurality of inlays placed within and between sections of the target. The target may be configured for a self-ionized plasma (SIP) deposition application or an ionized metal plasma (IMP) deposition application. The target may further include inlays comprised of pure elements. The target may be planar and may be circularly shaped. The inlays may be wedge-shaped, and may have equal surface areas, or contoured edges wherein the areal density of the wedge-shaped inlays increases non-linearly outwards from the center of the target. The inlays may also comprise wire-shaped or line-segmented configurations. The wire-shaped or line segmented inlays may be configured in a radial pattern extending outwards from the center of the target, and may comprise having a greater density of inlays closer to the center of the target than to an edge of the target. The inlays may also be button-shaped or disc-shaped. The button shaped inlays may be aligned in a circular pattern, such that the average density per unit area of the inlays remains constant as measured from the center to the edge of the target. The sputter target may comprise copper. The target may be configured such that the deposition of the target material and the inlay material leads to the production of alloy films deposited on the wafer, the alloy films comprising CuAl, CuBe, CuB, CuCd, CuCo, CuCr, CuIn, CuPd, CuSn, CuTa, CuTi, CuZr or CuZn. The target may include some inlays comprising pure elements and other inlays comprising metal alloys. The target may also be configured such that the target material and the inlay material leads to the production of alloy films deposited on the wafer, the alloy films including CoW, CoB, CoWB, and ternary alloys.
The inlays and the target sections may further comprise machined step-type patterns at respective adjoining surfaces. The machined tapered edges of the inlays are machined to expose greater surface area of the inlays on the target top surface.
In a second aspect, the present invention is directed to a sputter target apparatus for a magnetron cathode adapted to allow for a controlled sputtering process and produce a uniform metal alloy film on a semiconductor substrate having a target comprising a top surface, an outer edge, and a plurality of inlays comprised of metal alloys placed within and between sections of the target.
In a third aspect, the present invention is directed to a sputter target apparatus for a magnetron cathode adapted to allow for a controlled sputtering process and produce a uniform metal alloy film on a semiconductor substrate having a target comprising a top surface, an outer edge, and a plurality of inlays comprising pure elements and a plurality of inlays comprising metal alloys, placed within and between sections of the target.
In a fourth aspect, the present invention is directed to a method for constructing a planar sputter target apparatus for a magnetron cathode comprising: debonding target backing from the target; forming spaces within the target to accommodate inlays; bonding the backing plate to the target; cleaning the target; and, inserting the inlays within the formed spaces. The method further comprises forming spaces in a predetermined geometric pattern within the target for the inlays.